This invention relates to the field of automatic transmissions for motor vehicles. More particularly, the invention pertains to a kinematic arrangement of gearing, clutches, brakes, and the interconnections among them in such transmissions.
U.S. Pat. No. 5,106,352 describes a multi-speed automatic transmission for motor vehicles that includes two parallel gearsets providing two fixed speed ratios. The second speed ratio is higher than the first speed ratio. A first power path using the first fixed speed ratio includes a first control clutch and a second control clutch, and a second power path using the second fixed speed ratio includes a third control clutch. Several embodiments of the transmission include a double planetary gearset; other embodiments disclose a Ravigneaux gearset, a first control brake and a second control brake. Alternatively, the input shaft and output shaft are in alignment and one of the two speed ratios is a direct drive.
Optional axle ratios are used to improve towing. performance of heavy duty trucks. Although steeper axle ratios improve vehicle launch capability when the vehicle is loaded, these axle ratios produce lower fuel economy even when the vehicle is unloaded, and multiple axle ratios add complexity to the vehicle assembly process. In North America, operators of 4×4 trucks rarely use the Low Range in today's 4×4 applications that provide two- speed transfer cases. The transfer case clutch mechanism for selecting low-range and high-range operation on many transfer cases cannot be shifted unless the vehicle is stopped.